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From: David Howells <dhowells@redhat.com>
To: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk
Cc: dhowells@redhat.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	nicolas.dichtel@6wind.com, raven@themaw.net,
	Christian Brauner <christian@brauner.io>,
	keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-block@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Details on the UAPI of implementing notifications on pipes
Date: Tue, 05 Nov 2019 16:02:59 +0000	[thread overview]
Message-ID: <18580.1572969779@warthog.procyon.org.uk> (raw)
In-Reply-To: <157262963995.13142.5568934007158044624.stgit@warthog.procyon.org.uk>

So to implement notifications on top of pipes, I've hacked it together a bit
in the following ways:

 (1) I'm passing O_TMPFILE to the pipe2() system call to indicate that you
     want a notifications pipe.  This prohibits splice and co. from being
     called on it as I don't want to have to try to fix iov_iter_revert() to
     handle kernel notifications being intermixed with splices.

     The choice of O_TMPFILE was just for convenience, but it needs to be
     something different.  I could, for instance, add a constant,
     O_NOTIFICATION_PIPE with the same *value* as O_TMPFILE.  I don't think
     it's likely that it will make sense to use O_TMPFILE with a pipe, but I
     also don't want to eat up another O_* constant just for this.

     Unfortunately, pipe2() doesn't have any other arguments into from which I
     can steal a bit.

 (2) I've added a pair of ioctls to configure the notifications bits.  They're
     ioctls as I just reused the ioctl code from my devmisc driver.  Should I
     use fcntl() instead, such as is done for F_SETPIPE_SZ?

     The ioctls do two things: set the ring size to a number of slots (so
     similarish to F_SETPIPE_SZ) and set filters.

Any thoughts on how better to represent these bits?

Thanks,
David


      parent reply	other threads:[~2019-11-05 16:03 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-01 17:34 [RFC PATCH 00/11] pipe: Notification queue preparation [ver #3] David Howells
2019-11-01 17:34 ` [RFC PATCH 01/11] pipe: Reduce #inclusion of pipe_fs_i.h " David Howells
2019-11-01 17:34 ` [RFC PATCH 02/11] Remove the nr_exclusive argument from __wake_up_sync_key() " David Howells
2019-11-01 17:34 ` [RFC PATCH 03/11] Add wake_up_interruptible_sync_poll_locked() " David Howells
2019-11-01 17:34 ` [RFC PATCH 04/11] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
     [not found]   ` <20191107090306.GV29418@shao2-debian>
2019-11-07 16:51     ` [pipe] d60337eff1: phoronix-test-suite.noise-level.0.activity_level 144.0% improvement Linus Torvalds
2019-11-07 17:42     ` David Howells
2019-11-01 17:34 ` [RFC PATCH 05/11] pipe: Allow pipes to have kernel-reserved slots [ver #3] David Howells
2019-11-01 17:34 ` [RFC PATCH 06/11] pipe: Advance tail pointer inside of wait spinlock in pipe_read() " David Howells
2019-11-01 17:35 ` [RFC PATCH 07/11] pipe: Conditionalise wakeup " David Howells
2019-11-01 17:35 ` [RFC PATCH 08/11] pipe: Rearrange sequence in pipe_write() to preallocate slot " David Howells
2019-11-01 17:35 ` [RFC PATCH 09/11] pipe: Remove redundant wakeup from pipe_write() " David Howells
2019-11-01 17:35 ` [RFC PATCH 10/11] pipe: Check for ring full inside of the spinlock in " David Howells
2019-11-01 17:35 ` [RFC PATCH 11/11] pipe: Increase the writer-wakeup threshold to reduce context-switch count " David Howells
2019-11-01 19:24 ` [RFC PATCH 00/11] pipe: Notification queue preparation " Linus Torvalds
2019-11-01 22:05 ` David Howells
2019-11-01 22:12   ` Linus Torvalds
2019-11-05 16:02 ` David Howells [this message]

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